Hotel in Cologne that allows early check-in?

That is not a specific trait of any hotel. Just advise the hotel you will be arriving early. Will not be the first time as early arrivals are frequently. We just advise the hotel we are arriving early. Generally the room is available. Sometimes we have to wait an hour or so. In that case, we leave the luggage, and go for a walk -- maybe get a coffee.

I trust you know that Cologne is particularly known for how much is within walking distance of the HBF. That's why I like the (not so cheap) Hilton just across the street. But my point is that if you leave your bags at a hotel that can't put you right in a room, you don't need to learn the local transit system. Just start walking to the dozen or more major attractions within 1/2 mile of the HBF. Come back when they think the room will be ready.

Luggage lockers at the hbf

To add to Stephen's reply, if you're arriving at Köln Hbf, and if storage in the station is an option:

Köln Hauptbahnhof (Cologne central station)

• Train station, in English
• Luggage lockers, in English
• Station map, in German

"Schließfach" lockers are in D-Passage. The map shows there's also "Gepäckaufbewahrung" (luggage check room) in the southwest corner of the station.

You can request an early check in at most hotels but they can't be guaranteed due to occupancy and check out times.

To make sure there is a room waiting for you, make a reservation for the night before and your room will be ready. Just make sure the hotel knows what you are doing so you are not listed as a no-show.

You do not need to use lockers to store your bags!
Every hotel will hold your bags until check-in or after check out so you can go do things. Most hotels will let you check in early if the room is ready. Just send them an email and ask. Easy peasy.

As others have noted most hotels have a luggage room, where you can store your luggage before checkin. Just remember to have a lock on your bags.

The basic Ibis hotels have early check in anytime options for an additional fee.
https://all.accor.com/ssr/app/ibis/hotels/cologne-germany/index.en.shtml?dateIn=2023-01-19&nights=1&compositions=2&stayplus=false&snu=false&accessibleRooms=false

I have always been able to leave my luggage at the hotel if early check-in was not available. When I was there last May, I stayed at the City Class Europa am Dom hotel at Am Hof 34-46 in Cologne. It was a last minute booking and I was pleasantly surprised by how comfy and nice it was. It was 2 blocks from the train station, reasonably priced and I had a view of the Dom from my window. Best of all, it has air-conditioning, which I needed at that time.

When I got there, they could not check me in early but I was able to leave my bags there while I went out, had some lunch and explored the cathedral and other sites.

Thanks all for the replies. I think I have a plan now.